docs: def singularize(plural):
      """Convert plural word to its singular form.
  
      Args:
          plural: A word in its plural form.
      Returns:
          The word in its singular form.
      """
      if plural in UNCOUNTABLES:
          return plural
      for i in IRREGULAR:
          if i[1] == plural:
              return i[0]
      for i in SINGULARIZE_PATTERNS:
          if re.search(i[0], plural):
              return re.sub(i[0], i[1], plural)
      return plural